There is an on-vehicle apparatus control system in which control of an on-vehicle apparatus is performed, such as locking and unlocking of a door on the basis of radio signals which are transmitted and received between an on-vehicle control device mounted on a vehicle and a portable machine carried by a user. Communication methods between the on-vehicle control device and the portable machine are roughly classified into three methods such as a polling method, a passive entry method, and a keyless entry method.
In the polling method, the on-vehicle control device transmits a response request signal at a predetermined cycle regardless of a position of the portable machine. If the response request signal is received, the portable machine returns a response signal to the on-vehicle control device. In the passive entry method, when a user comes close to or comes into contact with a door knob, a passive request switch is turned on, and the on-vehicle control device transmits a response request signal to the portable machine. If the response request signal is received, the portable machine returns a response signal to the on-vehicle control device. In the keyless entry method, a response request signal is not transmitted from the on-vehicle control device to the portable machine, and, when the user operates the portable machine, a remote control signal is transmitted to the on-vehicle control device from the portable machine. In any case, if the response signal or the remote control signal is received from the portable machine, the on-vehicle control device performs collation between ID codes included in the signal. If the collation is successful, the on-vehicle control device locks or unlocks a door of the vehicle.
The on-vehicle control device is provided with an on-vehicle transmission unit which transmits a response request signal to the portable machine, and an on-vehicle reception unit which receives a response signal or a remote control signal from the portable machine. For example, as disclosed in JP-A-2009-144367, the on-vehicle transmission unit is provided in plurality inside a vehicle interior or on an outer surface of a vehicle. The on-vehicle reception unit may be provided alone in the vehicle interior of the vehicle. On-vehicle switch means such as an access switch is provided on an outer surface of a door of the vehicle.
In JP-A-2009-144367, in order for a response request signal transmitted from the on-vehicle transmission unit to be easily received by the portable machine located around the vehicle regardless of a position of the on-vehicle transmission unit, the transmission intensity of the response request signal transmitted from the on-vehicle transmission unit is switched according to the operated access switch. Specifically, in a case where the access switch located near the on-vehicle transmission unit is operated, the transmission intensity of a response request signal transmitted from the on-vehicle transmission unit is low. In a case where the access switch separated from the on-vehicle transmission unit is operated, the transmission intensity of a response request signal transmitted from the on-vehicle transmission unit is high.
Meanwhile, in a case of the polling method or the passive entry method, for example, an illegal communication act may be performed in which the portable machine which is far away imitates a state of being in close proximity to a vehicle as a result of a relay relaying a response request signal transmitted from the on-vehicle control device and the portable machine receiving the response request signal. The illegal communication act using the relay is called relay attack. A malicious third party who is not an owner of a vehicle may commit a crime such as theft of the vehicle by unlocking a door of the vehicle or starting an engine through the relay attack.
Therefore, regarding crime prevention countermeasures against the relay attack, for example, in JP-A-2010-121297, a distance between an on-vehicle transmission unit and a portable machine is calculated on the basis of the electric field intensity of a response request signal received by the portable machine, and a distance between the portable machine and an on-vehicle reception unit is calculated on the basis of the electric field intensity of a response signal received by the on-vehicle reception unit. In a case where there is a considerable difference between both of the distances, a door of a vehicle is not unlocked.
In JP-A-2010-121297, the portable machine lowers the transmission intensity of a response signal as a calculated distance between the on-vehicle transmission unit and the portable machine is short. As mentioned above, since the transmission intensity of a response signal from the portable machine is lowered, a signal transmitted from the portable machine which is far away from the vehicle is not received by the on-vehicle control device even if relay attack is performed, and thus the door of the vehicle is not unlocked.
If the transmission intensity of a response signal from a portable machine is low, relay attack can be prevented, but, on the other hand, communication performance between the portable machine carried by a legal user and an on-vehicle control device is reduced. Specifically, during passive entry, for example, in a case where a legal user operates on-vehicle switch means located at a position separated from the on-vehicle reception unit, the transmission intensity of a response signal transmitted from the portable machine carried by the user is low, and thus there is a concern that the response signal may not be received by the on-vehicle reception unit. In this case, the door of the vehicle is not unlocked and thus convenience of the passive entry disappears.